1. Field of the Invention
The present invention relates to gate valves having a movable gate selectively engageable with at least one valve seat to prevent flow through the valve, and at least one movable seat protector which selectively covers the valve seat.
2. Description of Related Art
In a gate valve, passage of fluid or material through the valve is controlled by selective movement of a gate into and away from contact with at least one valve seat. In the course of normal use, the valve seat typically becomes eroded, worn and/or corroded, requiring replacement.
Various attempts have been made to improve gate valves by overcoming or avoiding the deterioration of the valve seats. It has been proposed to provide removable valve seats which may be replaced without replacing the entire valve. For example, removable seat rings have been constructed which have an externally threaded portion which engages with internal threading in the wall of the flow path adjacent to the valve seat. Such gate valves have been found to be unsatisfactory, in that breakdown of removable valve seats often still requires replacement of the entire valve.